The present invention relates to an ignition plug for use in an automobile engine, and more particularly to a plug of the type having an air passage adapted to introduce auxiliary air into the engine cylinder during the exhaust stroke of an engine cycle to accelerate the exhaust of combustion gas.
An ignition plug with an air passage is known by Japanese Published Unexamined Patent Applications (Kokai Tokkyo Koho) Nos. 53-70233 and 55-84868, in which open air is introduced into the engine cylinder through a radial hole formed in the plug to accelerate the exhaust of combustion gas and prohibit the same from remaining in the cylinder. The auxiliary air, as introduced by the plug, is effective to improve combustion efficiency, reduce fuel consumption, and relieve exhaust-gas troubles.
The known plug has a radial hole as an air passage extending from the inlet in the outer periphery of the housing to the outlet which opens to a void space between the inner periphery of the housing and the outer periphery of the insulator. However, this leads to disadvantages, one of which is that the plug can not be formed with such an air passage without changing its fitting dimensions from a standard plug. Another disadvantage is that the radial hole readily becomes choked by dust because of having its inlet near the dusty surface of the cylinder head. The radial hole is too short to have a double-check valve or a similar lengthwise valve for overcoming engine vibrations.
In accordance with the present invention which is intended to provide a remedy for the disadvantages in the known plug as described above, the inventive plug comprises a tubular center electrode and a tubular terminal forming an air passage through the axes thereof and a check valve mounted in the center electrode to close the air passage when an inside pressure is above the open-air pressure and open the air passage when it is below the open-air pressure. The plug is somewhat different from a standard one in the center electrode and the terminal but is the same in its fitting dimensions as the standard plugs. The air passage has its inlet so separated from the cylinder head as to be unaffected by dust on the cylinder head and is long enough to contain a double-check valve that is resistible to engine vibrations.
It is an object of the invention to provide an improved ignition plug with an air passage which has the same fitting dimensions as a standard plugs.
It is another object of the invention to provide an improved ignition plug with an air passage which is unaffected by dust on the cylinder head.
It is a further object of the invention to provide an improved ignition plug with an air passage containing a check valve which resists engine vibrations.
For an understanding of the principles of the invention, reference is made to the following description of typical embodiments thereof as illustrated in the accompanying drawing.